JP2023500210A - High performance bright pupil eye tracking - Google Patents

Abstract

A method (800) and system for controlling one or more lighting devices in an eye tracker system (100) such that a measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast is herein disclosed. be written. The method (100) comprises: a. capturing an image of a subject (102) within a predetermined image capture period, the image including one or both of the subject's eyes; b. Illuminating one or both eyes of a subject from one or more illumination devices (108 and 110) within a predetermined image capture period, wherein at least one of the illumination devices (108 and 110): illuminating, positioned close enough to the lens of the camera to produce a bright pupil effect; c. at least one of the illumination devices (108 and 110) to produce an intensity of the bright pupillary reflection such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast; and selectively changing one output.
[Selection drawing] Fig. 8

Description

The present invention relates to lighting device control, and more particularly to lighting devices for eye trackers.

Embodiments of the present invention are specifically configured to illuminate a subject's face in order to extract facial features such as pupils under bright pupillary conditions. However, it will be appreciated that the invention is applicable in a broader context and other applications.

Many eye-tracking systems rely on the detection of pupil contours to accurately track the subject's gaze. In order to detect these contours, there must be enough contrast between the imaged pupil and the surrounding iris to identify the contours.

When the illuminator is placed far from the optical axis of the imaging camera, the pupil appears dark and there is a large contrast between the pupil and the surrounding bright iris.

Conversely, when the illuminator is placed near the optical axis of the imaging camera (typically within about 3.25 degrees of the camera optical axis), the pupil appears bright due to retroreflection from the eye. In some cases. In conventional photography, this appears as the familiar "red-eye" phenomenon due to the optical properties of the inner region of the eye. In infrared imaging, where a grayscale image is produced, this manifests as a "bright pupil" effect in which the pupil appears white or almost white, typically brighter than the iris.

Eye tracking can be performed using cameras and illuminators in both bright and dark pupil conditions. Under dark pupillary conditions eye tracking is more accurate as the pupil contrast is typically higher. However, in a typical dashboard-mounted driver monitoring system, a single illuminator or group of illuminators must be at least They are required to be placed approximately 2 cm apart. This directly leads to an increase in the size of the camera and lighting unit. As vehicle electronics become more sophisticated, available space on the vehicle dashboard becomes more and more expensive, and this trend is expected to continue with the advent of semi-autonomous driving.

Thus, there is a commercial desire to minimize the spatial footprint of vehicle driver monitoring systems. For this reason, in the future it may be advantageous to implement bright pupil eye tracking systems.

To achieve a bright pupil image, the angular separation between the camera and the illuminator must be very small. Such small spacing is not only a major challenge for lens and illuminator design, but also creates a situation of total internal reflection that causes problems. In particular, under this camera/illuminator geometry, the pupil and iris are imaged at approximately the same luminance, which results in very low pupil contrast. These situations are called "gray pupil" situations. Any distance within the above range will cause a gray pupil situation in some scenarios. Without the contrast between the pupil and the iris, it is impossible to pinpoint the location of the pupil.

Any discussion of background art throughout the specification should in no way be construed as an admission that such technology is well known or forms part of the general general knowledge known in the art.

According to a first aspect of the present invention, a method is provided for controlling one or more lighting devices in an eye tracker such that a measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast. , this method gives
capturing an image of the subject, including one or both of the subject's eyes, for a predetermined image capture period;
illuminating one or both of the subject's eyes from one or more illumination devices during the predetermined image capture period,
illuminating, wherein the at least one lighting device is positioned close enough to the lens of the camera to produce a bright pupil effect;
selectively outputting the output of at least one of said illuminators to produce a bright pupil reflection intensity such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast; including changing to

In one embodiment, the output of at least one of the illuminators is a direct measure of pupil/iris contrast determined by the intensity of pixels in the pupil region relative to the iris region of one or both eyes of the subject. is selectively varied based on In an embodiment, the output of at least one of the lighting devices is
i. ambient light measurements,
ii. a measurement of the subject's pupil diameter, and/or iii. selectively varied based on one or more of the subject's current or recent viewing directions.

In one embodiment, the ambient light measurements are derived from exposure settings of the camera and/or lighting settings of the one or more lighting devices.

In one embodiment, the output of at least one of the lighting devices is selectively varied based on a measurement of pupillary contrast of the subject's eye from a previous image capture period. In one embodiment, the output of at least one of the lighting devices is selectively varied based on physiological parameters of the subject. In one embodiment, the output of at least one of the lighting devices is selectively varied at at least two different power levels during image capture.

In one embodiment, the camera captures at least two images within an image capture period, and the two images are captured using different lighting or image capture settings. In some embodiments, the first image is captured while the one or more lighting devices have a first power level and the second image is captured while the one or more lighting devices have a second power level different from the first power level. Captured while having a level.

An embodiment includes performing image subtraction on the two images to produce a resulting image with increased pupillary contrast.

In one embodiment, the eye tracker includes a single lighting device. In an embodiment the controller is arranged to modulate the illumination power of said illumination device during the image capture period. In one embodiment, the eye tracker includes two lighting devices positioned at different distances from the camera. Preferably, each illuminator is placed close enough to the lens of the camera to produce a bright pupil effect, but at a different distance from the lens to produce different bright pupil reflection characteristics. .

In an embodiment, selectively varying the output of at least one of the lighting devices includes deactivating one of the two lighting devices during an image capture period.

According to a second aspect of the present invention, there is provided a method of controlling two or more lighting devices in an eye tracker such that the measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast, comprising: This method
capturing an image of a subject, said image including one or both of said subject's eyes, within a predetermined image capture period;
illuminating one or both eyes of the subject within the predetermined image capture period from a system of two or more illuminators, each of the illuminators for producing a bright pupil effect; illuminating with an illuminator placed close enough to the lens of the camera, but at different distances from said lens to produce different bright pupil reflection characteristics;
selecting the outputs of the two or more illuminators to produce a characteristic bright pupil reflex such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast. including changing

According to a third aspect of the present invention, there is provided a system for controlling one or more lighting devices in an eye tracker such that the measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast. and this system
a camera configured to capture an image of a subject within a predetermined image capture period, the image including one or both of the subject's eyes;
one or more lighting devices configured to selectively illuminate one or both eyes of the subject during the predetermined image capture period, at least one of the lighting devices being a bright pupil a lighting device positioned close enough to the lens of the camera to produce an effect;
said output of at least one of said illumination devices such that a measured pupil/iris contrast in a captured image produces an intensity of bright pupillary reflex such that it exceeds a predetermined minimum value of pupil/iris contrast; a controller configured to selectively vary the .

In some embodiments, the system includes one lighting device. Preferably, the illumination device is placed within a distance of 7 mm-15 mm from the camera. More preferably, the illumination device is placed at a distance of 8 mm-14 mm from the camera. In other embodiments, the system includes two lighting devices. Preferably, each illuminator is placed close enough to the lens of the camera to produce a bright pupil effect, but at a different distance from the lens to produce different bright pupil reflection characteristics. .

According to a fourth aspect of the present invention, there is provided a system for controlling two or more illuminators in an eye tracker such that the measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast. and this system
a camera configured to capture an image of a subject within a predetermined image capture period, the image including one or both of the subject's eyes;
two or more lighting devices configured to illuminate one or both eyes of the subject within the predetermined image capture period, each of the lighting devices to produce a bright pupil effect; an illuminator positioned close enough to the lens of the camera, but positioned at different distances from the lens so as to produce different bright pupil reflex characteristics;
selectively combining the outputs of two or more illuminators to produce a characteristic bright pupil reflex such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast. including a controller configured to vary.

In one embodiment, the system includes two lighting devices. Preferably, a first illumination device is arranged at a distance of 3 mm-15 mm from said camera and a second illumination device is arranged at a distance of 7 mm-50 mm from said camera. More preferably, the first illumination device is arranged at a distance of 8 mm-13 mm from said camera and the second illumination device is arranged at a distance of 20 mm-30 mm from said camera.

In an embodiment, said controller is configured to deactivate one of said lighting devices during an image capture period.

In some embodiments, the bright pupillary reflex characteristic includes a measurement of the retroreflection effect by one or both eyes of the subject. In one embodiment, the bright pupil reflex characteristic comprises a direct measure of pupil/iris contrast determined by the intensity of pixels in the pupil region relative to the iris region of one or both eyes of the subject.

According to a fifth aspect of the invention there is provided an illumination system for an eye tracker, the system comprising:
a camera configured to capture an image of a subject within a predetermined image capture period, the image including one or both of the subject's eyes;
one or more lighting devices configured to selectively illuminate one or both eyes of the subject during the predetermined image capture period, at least one of the lighting devices being a bright pupil a lighting device positioned close enough to the lens of the camera to produce an effect;
A controller, said controller comprising:
processing the captured images to measure the pupillary contrast of the subject's eye in at least a subset of the images;
One or more illuminations based on the signal controlled to produce an intensity of the bright pupillary reflex such that the measured pupil/iris contrast in the captured screen exceeds a predetermined minimum pupil/iris contrast. and a controller configured to control the output of the device, wherein the control signal is derived based on a pupillary contrast measurement from a previous image capture period. .

According to a fifth aspect of the invention, there is provided an eye tracking system, the system comprising:
a camera configured to capture an image of a subject within a predetermined image capture period, the image including one or both of the subject's eyes;
one or more lighting devices configured to selectively illuminate one or both eyes of the subject during the predetermined image capture period, at least one of the lighting devices being a bright pupil a lighting device positioned close enough to the lens of the camera to produce an effect;
A controller, said controller comprising:
processing the captured image to perform an eye-tracking routine to track the eyes of the subject, the eye-tracking routine including determining one or more control parameters;
one or more based on one or more control parameters to generate an intensity of the bright pupillary reflex such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast. and a controller configured to:

In one embodiment, the control parameter is
i. ambient light measurements,
ii. a measurement of the subject's pupil diameter, and/or iii. including the subject's current or recent gaze direction;

In some embodiments, the control parameters include physiological parameters of the subject.

In an embodiment, the processor is configured to process the captured image to determine a pupillary contrast measurement of an eye of the subject, wherein the pupillary contrast measurement from said previous image capture period comprises: It is used as a control parameter for controlling the lighting power of one or more lighting devices. Thus, in any of the described embodiments, pupillary contrast measurements from previous image capture periods are parameters or factors upon which the illumination power of at least one of the illumination devices is selectively varied. obtain.

Exemplary embodiments of the present disclosure will now be described, by way of example, with reference to the accompanying drawings.
FIG. 1 is a perspective view of the interior of a vehicle having a driver monitoring system including a camera and two LED light sources mounted inside the vehicle. Figure 2 is a perspective view of a driver looking into the dashboard of a vehicle having the driver monitoring system of Figure 1 mounted on the dashboard of the vehicle. 3 is a schematic functional diagram of the driver monitoring system according to FIGS. 1 and 2. FIG. FIG. 4 is a schematic diagram of an eye illuminated by an infrared illuminator to illustrate the bright pupil effect. FIG. 5 is a schematic illustration of exemplary bright and dark pupil effect situations and associated images. FIG. 6 is a plan view of the driver monitoring system of FIGS. 1-3 showing the camera field of view and the LED illumination field of view for the subject. FIG. 7 is a plan view of the driver monitoring system of FIGS. 1-3 showing the lighting geometry and imaging geometry for the subject being imaged. FIG. 8 is a process flow diagram illustrating major steps in an illumination method for an eye tracker. FIG. 9 is an exemplary setup for a first embodiment of a camera and a pair of LEDs. FIG. 10 is a driver's perspective view of a vehicle dashboard having a driver monitoring system with a single LED mounted on the vehicle dashboard. FIG. 11 is a schematic functional diagram of the driver monitoring system of FIGS. 1-3 showing data flow between different system elements. FIG. 12 illustrates an exemplary situation where illumination from far-side LEDs is preferred. FIG. 13 illustrates an exemplary situation where illumination from near-side LEDs is preferred. FIG. 14 illustrates graphs of the detected iris and pupil contrast as a function of infrared light source and camera visual angle for four different pupil sizes.

The lighting systems and lighting methods described herein can be applied and used in many eye tracking environments. An example is the monitoring of drivers or passengers of automobiles or other vehicles such as buses, trains or planes. In addition, the system described can be applied to operators using or operating any other equipment such as machines and flight simulators. For ease of understanding, embodiments of the invention are described herein in the context of driver monitoring systems for vehicles. Furthermore, although the illumination device is described as being a light emitting diode (LED), it will be appreciated that the invention is applicable to other types of light sources, such as vertical cavity surface emitting lasers (VCSELs). .
[Overview of the system]

Referring initially to FIGS. 1-3, a driver monitoring system 100 for capturing images of a vehicle driver 102 while operating a vehicle 104 is illustrated. The system 100 may apply various image processing algorithms to captured images, such as face detection, facial feature detection, face recognition, facial feature recognition, face tracking, or facial feature tracking such as tracking a person's eyes. further configured to run Exemplary image processing parameters are described in U.S. Pat. No. 7,043,056 by Edwards et al. entitled "Facial Image Processing System" and assigned to Seeing Machines Pty Ltd (hereinafter "Edwards et al."), The contents of which are hereby incorporated by cross-reference.

As best illustrated in FIG. 2, the system 100 is positioned on or within an instrument display of a vehicle dashboard 107 to identify and locate one or more human facial features. , and tracking, an imaging camera 106 oriented to capture an image of the driver's face in the infrared wavelength region.

Camera 106 is a conventional CCD or CMOS-based with a two-dimensional array of light sensitive pixels (or photodetectors) and optionally the ability to determine range or depth (such as through one or more phase detection elements). digital camera. Photosensitive pixels are capable of sensing electromagnetic radiation, at least in the infrared region. Camera 106 may also be a three-dimensional camera, such as a time-of-flight (TOF) camera, or other scanning or range-based camera capable of imaging a scene in three dimensions. In other embodiments, camera 106 may be replaced by a pair of similar cameras that operate in a stereo configuration and are calibrated to extract depth information of subjects in images captured by camera 106 . Camera 106 is preferably configured to image in the infrared wavelength region, although it will be appreciated that in alternate embodiments camera 106 may image in the visible region. Although not shown, the camera 106 also includes imaging optics, including a first imaging lens, for focusing light onto the array of light sensitive pixels.

Still referring to FIG. 2, in the first embodiment, system 100 also includes a pair of infrared lighting devices in the form of light emitting diodes (LEDs) 108 and 110, which are positioned on dashboard 107 of the vehicle. They are placed in their respective positions in close proximity to the cameras and horizontally spaced apart. As described below, LEDs 108 and 110 are positioned at different distances from camera 106 . In other embodiments described below, only a single LED is used. Also, in some embodiments, more than two light sources may be employed in the system.

To improve imaging of the driver's face so that a high quality image of the driver's face or facial features can be obtained, the LEDs 108 and 110 are illuminated during a predefined image capture period during which the camera 106 is capturing images. , is configured to illuminate the driver 102 with infrared radiation. Operation of camera 106, LEDs 108 and 110 in the infrared region reduces visual distraction for the driver. The operation of camera 106 and LEDs 108 and 110 is controlled by an associated controller 112 which includes a computer processor or microprocessor and memory for storing and buffering captured images from camera 106 . In other embodiments, instead of LEDs, different types of light sources such as VCSELs may be used.

As best illustrated in FIG. 2, camera 106 and LEDs 108 and 110 may be manufactured or assembled as a single unit 111 having a common housing. This unit 111 is shown mounted on the vehicle dashboard 107, but may be installed during manufacture of the vehicle, or may be installed later as an aftermarket product. In other embodiments, the driver monitoring system 100 includes one or more cameras positioned in any suitable location to capture images of the head or facial features of the driver, subject, and/or passengers within the vehicle. and a light source. By way of example, the cameras and LEDs may be located on the vehicle's steering column, rearview mirror, center console, or driver's side front pillar. In the illustrated embodiment, the first light source and the second light source each include a single LED. In other embodiments, each light source may each include multiple individual LEDs.

Turning now to FIG. 3, the functional elements of system 100 are schematically illustrated. System controller 112 functions as the central processing unit of system 100 and is configured to perform several functions described below. The controller 112 is located within the dashboard 107 of the vehicle 104 and may be coupled or integrated with the vehicle's on-board computer. In another embodiment, controller 112 may be placed in a housing or module along with camera 106 and LEDs 108 and 110 . This housing or module may be sold as an aftermarket product, mounted on a vehicle dashboard, and then calibrated for use in that vehicle. In further embodiments, such as flight simulators, controller 112 may be an external computer or unit, such as a personal computer.

Controller 112 may be any form of computer processing device or such that processes electronic data, e.g., from registers and/or memory, and transforms the electronic data into other electronic data that may be stored, e.g., in registers and/or memory. can be implemented as part of a As illustrated in FIG. 3, the controller 112 includes a microprocessor 114, which includes random access memory (RAM), read-only memory (ROM), electronically erasable programmable read-only memory (EEPROM). , and other equivalent memory or storage systems that will be readily apparent to those skilled in the art.

Microprocessor 114 of controller 112 includes vision processor 118 and device controller 120 . Vision processor 118 and device controller 120 both represent functional elements executed by microprocessor 114 . However, it will be appreciated that in alternate embodiments, the vision processor 118 and the device controller 120 may be implemented as separate hardware, such as a microprocessor used in conjunction with custom or specialized circuitry.

Vision processor 118 is configured to process the captured images to perform driver monitoring. For example, driver monitoring is determining the three-dimensional head pose and/or line-of-sight position of the driver 102 within the monitoring environment. To accomplish this, vision processor 118 utilizes one or more line-of-sight determination algorithms. This may include, by way of example, the methods described in Edwards et al. The vision processor 118 determines driver 102 attributes such as eye closure, blink rate, and driver 102 to detect driver attention, drowsiness, or other problems that may interfere with the driver's safe vehicle operation. Various other functions may also be performed, including tracking head movements.

Raw image data, gaze position data, and other data acquired by vision processor 118 are stored in memory 116 .

The device controller 120 controls various parameters of the camera 106, such as shutter speed and/or image sensor exposure/integration time, synchronizing the exposure time of the camera 106, or more generally pre-defined image processing. It is configured to selectively activate the LEDs 108 and 110 in the manner described below during the capture period. LEDs 108 and 110 are preferably electrically coupled to device controller 120, although they may also be wirelessly controlled by controller 120 through wireless communications such as Bluetooth™ or WiFi™ communications. good.

Thus, during operation of vehicle 104, device controller 120 activates camera 106 to capture images of driver's 102 face in the form of a video sequence. LEDs 108 and 110 are activated and deactivated synchronously with the image frames captured by camera 106 to illuminate the driver for a predefined image capture period. The device controller 120 and the vision processor 118 work together to capture images of the driver to obtain information on the driver's condition, such as drowsiness, alertness, and gaze position during normal operation of the vehicle 104. , and provide to process. Device controller 120 and vision processor 118 also cooperate to perform dynamic lighting control as described below.

Additional components of the system may also be included in the common housing of unit 111 or provided as separate components according to other additional embodiments. In one embodiment, the operations of controller 112 are performed by an onboard vehicle computer system that is coupled with camera 106 and LEDs 108 and 110 .

Throughout this specification, specific functions performed by vision processor 118 or device controller 120 may be more broadly described as being performed by controller 112 .
[Bright pupil condition]

Referring now to FIG. 4, a schematic diagram of the bright pupil condition is shown. With reference to this figure, the concept of the bright pupil condition is described.

When a point light source such as infrared LED 400 is used to illuminate eye 402 , lens 404 of eye 402 images the point light source into image 406 on the surface of retina 408 . Since lens 404 is an imperfect lens, image 406 becomes a blurred disc on retina 408 . Some light is diffusely reflected from retina 408 and a subset of this light is incident on lens 404 . A subset of this reflected light is focused back to the light source by lens 404 . Again, due to imperfections in lens 404 , the reflected light is imaged as a finite diameter disk around LED 400 rather than an ideal point. The disc represents a region 410 where the captured image would exhibit a bright pupil effect.

Since only light that passes through the pupil 412 of the eye can enter the interior of the eye 402, the bright pupil area defined by region 410 decreases as the pupil diameter decreases and the brightness decreases. The position, shape, and size of image 406 on retina 408 change as the eye rotates to look at different areas in space (different gaze angles). As a result, the size and brightness of region 410 varies with viewing angle.

The bright pupil effect is
Enlarging the pupil (size),
・Gaze angle to the camera,
• Affected by many factors, including age and ethnicity of the subject, and • wavelength of light.

Under the bright pupil effect, the pupil is brighter than the surrounding iris in a grayscale image. When imaged by a camera, the iris appears to be the dark area around the very bright pupil. This is illustrated in the left part of Figure 5, which also shows an exemplary angle at which the eye is illuminated. The right part of FIG. 5 illustrates the more common dark pupil condition where the pupil is darker than the surrounding iris.

Considering the physiology of the human eye, the bright pupil effect typically appears when the imaging camera is placed relative to the eye at an angle of less than 3.25 degrees from the light source. However, it will be appreciated that the specific angles at which the bright pupil effect appears will vary with the above and other factors.

6 and 7, top views of driver monitoring system 100 are illustrated. FIG. 6 illustrates the illuminated areas of LEDs 108 and 110 and the field of view of camera 106 . FIG. 7 illustrates the geometric angle between camera 106 and LEDs 108 and 110, including the camera optical axis. Under normal driving conditions, camera 106 and LEDs 108 and 110 are typically placed at a distance of between 30 cm and 80 cm from driver's 102 face. To achieve a bright pupil condition (LEDs 108 and 110 illuminating driver 102 at an angle of less than 3.25 degrees (θ1 and θ2 in FIG. 7) from the optical axis of camera 106), LEDs 108 and 110 should be about 30° from camera 106. should be placed within mm. However, the outer LEDs 110 may be placed at a distance of up to about 50 mm from the camera 106 lens.

For a given value of the angular separation between the camera and the illuminator, the larger the pupil size, the higher the brightness of the pupil. Similarly, for a given value of camera/illuminator angle, a subject looking straight into the camera will have a darker pupil than when the subject is looking off-axis.

When there is substantial ambient illumination, the contrast between the bright pupil and the iris is determined by the brightness of the pupil and the brightness of the iris. The brightness of the pupil is mostly due to the bright pupil effect due only to the controlled illumination from the LEDs. Ambient light does not significantly affect the intensity of the bright pupil. The iris brightness is due to a combination of controlled lighting and ambient lighting.

Therefore, it will be appreciated that in other monitoring environments and under different conditions, LEDs 108 and 110 may be placed at a greater distance from camera 106 to still achieve bright pupil conditions.

As mentioned above, there is a situation called a "gray pupil" situation where the iris and pupil are imaged with approximately the same intensity and the contrast of the pupil is very low. Typically, gray pupils occur only when the pupil size is small (when pupil brightness is relatively low), so gray pupils typically occur under bright visible ambient conditions (iris brightness is generally high).

gray pupil situation
- Varying the intensity of the bright pupil effect (e.g. by moving the illumination source closer or further away from the lens of the imaging camera);
It can be reduced by: adjusting the intensity of the controlled lighting; and adjusting the intensity of the ambient light.

It is also possible to change the pupil/iris contrast by changing the exposure period of the imaging camera, such as by changing the integration time (shutter period) of the sensor. However, the inventors have found that dynamically controlling the illumination power is advantageous because there is no added complexity or required changes in the exposure control loop of the device controller 120 control algorithm. I found it. Dynamically controlling illumination power is disclosed in PCT Patent Application Publication No. WO2019/084595 entitled "System and Method for Improving Signal to Noise Ratio in Object Tracking Under Poor Light Conditions" by Noble and assigned to Seeing Machines Pty Ltd. (hereinafter "Noble"), it is also advantageous for improving the signal-to-noise ratio in subject tracking under poor lighting conditions. Dynamic lighting control may also be performed in conjunction with dynamic exposure control to improve system performance under certain conditions, but at the cost of increased complexity of the control algorithm.
[Lighting control]

Referring now to FIG. 8, major steps in an illumination method 800 for ensuring that minimum pupil/iris contrast of the pupil and iris of the eye is maintained in an eye tracker system such as system 100 are shown. A process flow diagram is shown. Method 800 includes, at step 801, configuring camera 106 to capture an image of subject 102 during a predefined image capture period. The predefined image capture period may represent a normal shutter period for camera 106 operating at a normal frame rate. However, camera 106 may be configured to operate in a higher frame rate mode in which multiple integrations of the image sensor occur during a single shutter period. Similarly, some cameras are configured to record multiple images during a single shutter period using multiple image sensors while storing image data. Here, the predefined image capture period may represent multiple periods of sensor integration. Thus, it is also possible for multiple images to be captured within a single image capture period. The term "image capture period" is intended to cover all variations of image capture, whether it is the standard frame rate of the sensor integration mode of camera 106 or a higher frame rate.

The captured image includes one or both of the subject's eyes. In some eye tracker systems, eye tracking for each eye is performed independently, while in other eye tracker systems both eyes are tracked simultaneously. Only one eye may be tracked when both eyes cannot be tracked in an image frame. When neither eye can be tracked (eg, when the subject's eyes are closed), that image frame may be discarded for eye tracking purposes and a subsequent image read.

At step 802, one or both of the subject's eyes are illuminated by one or both of LEDs 108 and 110 for a predefined image capture period. In practice, steps 801 and 802 are performed synchronously with each other so that illumination occurs during a predefined image capture period.

In step 803, controller 112 controls LEDs 108 and 110 to produce an intensity of the bright pupil reflex such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast. selectively changing the output of at least one of As part of this step, vision processor 118 may calculate pupil/iris contrast from current or past images. This contrast calculation is described in detail below.

As described in more detail below, the present invention includes different embodiments having different combinations of LED groups (or other lighting devices). In a first embodiment, illustrated in FIGS. 1-3, 6 and 7, two LEDs (108 and 110) are provided, each LED directed to the lens of camera 106 to produce the bright pupil effect. Close enough, but placed at different distances from the lens to produce different bright pupil reflex characteristics. By way of example, the configuration of this first embodiment is illustrated schematically in FIG. 9, where LED 108 is positioned at a distance of 9 mm from the lens of camera 106 and LED 110 is positioned at a distance of 50.3 mm from the lens of camera 106. placed in

It will be appreciated that other arrangements of the LEDs 108 and 110 are possible to produce the bright pupillary effect and to produce different bright pupillary reflection characteristics. As an example, the near side LED 108 may be positioned within about 3 mm-15 mm from the camera 106 lens, and the far side LED 110 may be positioned within about 7 mm-50 mm from the camera 106 lens. may be placed in In some embodiments, the near side LED 108 is positioned within about 8 mm-13 mm from the camera 106 lens and the far side LED 110 is positioned within about 20 mm-30 mm from the camera 106 lens. It is preferably located within

The optimal separation between camera 106 and LEDs 108 and 112 depends on physical limitations of the camera lens and LED/secondary optics, and the presence and design of cover glasses (to avoid excessive internal reflections). It will also be understood that it depends on factors.

In the second embodiment system 200 illustrated in FIG. 10, only a single LED 108 is used to illuminate one or both eyes of the subject. A single LED 108 is placed close enough to the lens of the camera 106 to produce a bright pupil effect. In both embodiments, the LEDs are arranged such that the intensity of the bright pupillary reflex is such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast. They are dynamically driven by controller 112 to selectively change their outputs. Achieving a minimum pupil/iris contrast improves the performance of the eye-tracking system to correctly detect and track the line of sight of the subject being imaged.

Both of these embodiments are described below. It will be appreciated that each embodiment is only concerned with controlling LEDs (or more generally lighting devices) placed sufficiently close to the lens of the camera to induce the bright pupil effect. . This is unlike other illumination systems that operate in dark pupil conditions well off the camera's optical axis because the light source can be located far from the camera's lens.
[Embodiment 1--Lighting with two LEDs]

Referring again to FIG. 9, each illuminator is positioned close enough to the lens of the camera 106 to produce the bright pupil effect (as described above), but is positioned close enough to the lens of the camera 106 to produce different bright pupil reflection characteristics. are placed at different distances from the lens. Bright pupil characteristics include a measure of the magnitude of the retroreflection effect experienced by the illuminated eye. The magnitude of the retroreflective effect can be quantified by measuring the pupil and iris pixel values at different illumination positions for a given LED power. This can be measured in some embodiments as a measure of luminance or pixel intensity of one or more pixels in the iris region and one or more pixels in the pupil region in the captured image. These luminance measurements are performed by vision processor 118 during image processing of raw image data from camera 106 .

The luminance measurement is represented by a grayscale luminance measurement, typically in the captured image (eg, 16-bit) format. This brightness measurement may comprise the average brightness value of a plurality of pixels determined to be located in each of the iris and pupil of the image. For example, in a dark pupil situation, the raw 16-bit pupil luminance might be 3,540 and the iris luminance might be 18,050. In the bright pupil situation, the raw 16-bit pupil luminance might be 32,501 and the iris luminance might be 3,460. The determination of different eye regions is performed by vision processor 118 by known image processing techniques such as edge detection, shape recognition and contour detection.

The determination of iris and pupil regions can be performed as part of a more general eye-tracking algorithm, such as the algorithm described in Edwards et al. Typically, however, these regions may be identified by image processing techniques such as edge detection, shape recognition and Hough transform. Thus, within an image, the iris and pupil regions can be defined as a two-dimensional region or group of regions made up of individual pixels.

Pupil/iris contrast measurements may be performed by comparing luminance values of one or more pixels within the defined pupil region to luminance values of one or more pixels within the defined iris region. A pixel sample can be a single pixel from the respective region, a group of pixels distributed around the respective region, or an average pixel value of some or all of the pixels within the respective region.

Referring now to FIG. 11, a variation of FIG. 3 showing various data communicated between different elements of system 100 is illustrated. Here, vision processor 118 is shown receiving raw image data from camera 106 and sending various data to device controller 120 . Although memory 116 is not shown in FIG. 11 for simplicity, data communication between camera 106, vision processor 118, and device controller 120 may include storage and retrieval of data in memory 116. FIG.

During lighting control step 803 of method 800, controller 112 controls the output of one or both of LEDs 108 and 110 based on generated control signals 130 and 132, respectively. Control signals 130 and 132 include current and/or voltage signals determined by device controller 120 to drive corresponding LEDs to generate infrared radiation. Typically, LED groups are controlled using pulsed outputs with defined peak powers and pulse widths. In system 100 , the pulse width is set by device controller 120 to substantially match the exposure time of camera 106 .

Variations in output by the device controller 120 cover variations such as varying the pulse peak value, pulse shape, or pulse width. In some embodiments, the LED groups are controlled such that the energy content of the pulses is varied by device controller 120 . In other embodiments, the energy content of the pulse remains constant, but the pulse peak value and/or pulse shape is varied. By way of example, LED groups may be controlled dynamically based on pulsing curves, as described in the Noble publication referenced above.

The control signal sought by device controller 120 may be based on one or more of the following inputs.
Ambient Light Measurements Ambient light measurements may be obtained from an external ambient light sensor 150 and provided to the device controller 120 . Alternatively, ambient light measurements may be estimated by vision processor 118 from captured images through comparison of background features for many images. Vision processor 118 may implement algorithms that extract ambient light measurements from captured images by considering the reflectance of objects, the distance to objects, and the amount of controlled lighting. If the object being measured is fixed relative to the camera (such as an object in a vehicle interior), the distance factor remains constant. In some embodiments, a proxy measurement of ambient light is derived from the camera 106 exposure settings and/or the LED group illumination settings. Since cameras have built-in hardware and software configured to control image exposure times based on lighting conditions, using these exposure settings can be used as a proxy measure of ambient light. may be As an example, in scenes with low ambient light conditions, the camera 106 automatically detects the light level via the image sensor and sets a longer image exposure time.
A measurement of the subject's pupil diameter This is measured by the vision processor 118 from a previous image in which the pupil diameter is discernible. A larger diameter pupil indicates a lower amount of ambient light, and a smaller pupil indicates a higher amount of ambient light. A measurement of pupil diameter may also be used as a surrogate measurement of the ambient light present.
Current or recent viewing direction of the subject. The complex geometry of the human eye means that different areas of light incidence have different reflection characteristics. When the eye is looking straight at the light source, a strong retroreflection occurs and the bright pupil effect appears. However, at different viewing angles away from the light source, different reflection characteristics appear and may or may not result in a bright pupil effect. Furthermore, because the geometry of the eye varies from person to person, these characteristics also vary from person to person. Thus, the current or recent gaze direction as measured by driver monitoring system 100 may be utilized as input for controlling LEDs 108 and 110 .
Physiological parameters of the subject Human individuals of different ages and ethnicities have different eye geometries than others, with variations in eye size. In particular, the size of the human lens and the amount of pupil dilation can vary from person to person. This results in different bright and dark pupillary responses for a given optical system. Exemplary physiological parameters that vary from person to person include the size, shape, and reflectance of the fundus or lens, and the shape and response of the pupil. In some embodiments, these parameters may be input to device controller 120 and considered in determining appropriate control signals 130 and 132 . In some embodiments, these physiological parameters are measured directly. In other embodiments, physiological parameters are fitted by optimizing parameters based on training data and the like.
Direct Measurement of Pupil Contrast In an embodiment, the vision processor 118 is configured to process the captured images to determine a measure of the pupil contrast of the subject's eye. This measure of pupil contrast, which may be obtained from current or past captured images, may form an input to the device controller 120 to control the output of the LEDs 108 and 110. In some embodiments, as described above, a pupil contrast measurement is obtained by combining the luminance values of one or more pixels within the defined pupil region with the luminance values of one or more pixels within the defined iris region. is obtained by comparing with In other embodiments, pupil contrast may be derived by other techniques, such as determining the slope of pixel values from the iris region to the pupil region.

Device controller 120 includes one or more algorithms that generate desired control signals 130 and 132 for LEDs 108 and 110 based on one or more of the above inputs. A specific voltage or current value for the control signal may be based on a combination of the above measured inputs determined by the control algorithm. In some embodiments, controller 120 operates specific control algorithms that set desired voltages and/or currents for LEDs 108 and 110 based on the measured inputs. In one embodiment, each input is weighted based on importance.

Typically, in a dark environment (low ambient light), the near side LED 108 may be activated and the far side LED 110 may be deactivated. For dilated pupils, the upper bound on the angular separation between the camera and the LED may be larger, which alleviates the problem of internal reflections. In situations where the pupil size is small but the subject is looking in an off-axis direction, or where the pupil size is large enough, it is preferable to activate the near side LED 108 to increase the pupil/iris contrast. .

Typically, in bright environments (high ambient light), the far side LED 110 may be activated and the near side LED 108 may be deactivated. For a constricted pupil, the lower bound on the angular separation between the camera 106 and the LEDs 108 and 110 may be smaller, meaning that the camera assembly size is smaller. In situations where the subject is looking at the camera 106, or where the pupil size is small enough, the far side LED 110 may also be activated.

FIG. 12 illustrates an exemplary situation in which illumination from far-side LEDs 110 is preferred, and FIG. 13 illustrates an exemplary situation in which illumination from near-side LEDs 108 is preferred. Note that there is some overlap between FIGS. 12 and 13. FIG. This means that either the near side LED 108 or the far side LED 110 may be activated in some situations. For a given LED position and pupil size, if the subject looks straight into the camera, the pupil will be darker than when the subject looks in other directions.

Thus, at step 803, the device controller may implement control signals 130 and 132 such that the following exemplary lighting conditions are provided.
• LED 108 is activated and LED 110 is deactivated.
• LED 110 is activated and LED 108 is deactivated.
• The output of LED 108 is increased and LED 110 is deactivated.
• The output of LED 110 is increased and LED 108 is deactivated.
- LED 108 power is increased and LED 110 is decreased.
- LED 110 output is increased and LED 108 is decreased.
• LED 108 output is reduced and LED 110 is deactivated.
• The output of LED 110 is reduced and LED 108 is deactivated.

It will be appreciated that the lighting conditions above are merely exemplary and not an exhaustive list of possible conditions. The amount by which each LED is incremented or decremented may be based on a combination of the above inputs. In some embodiments, each LED can be driven at one of several predefined voltage or current levels based on the specific value or range of the detected input. In some embodiments, device controller 120 varies the illumination power of one or more illumination devices to at least two different power levels during the image capture period.

It will be appreciated that in other embodiments, system 100 includes more than two groups of LEDs arranged to produce a bright pupil effect.
Embodiment 2--Single LED

Referring now to FIG. 10, system 200 represents a second embodiment in which only near side LEDs 108 are implemented. In this embodiment, the LEDs 108 are preferably placed at a distance of 3 mm-15 mm from the lens of the camera 106, but this need not be the case.

This single LED embodiment only dynamically adjusts the intensity of the LED's controlled illumination until the ratio of ambient light to controlled light restores the pupil/iris contrast to a minimal level. can mitigate the presence of the gray pupil effect without changing the illumination angle. Here, controlled light represents the amount of light generated from LED 108 in a controlled manner, and ambient light represents all other light imaged by the photosensor array of camera 106 .

Dynamic control of LEDs 108 (and also LEDs 110 in the first embodiment) may be performed by device controller 120 based on the following understanding.
i. In low ambient light conditions, the pupil is large, but decreases in size as ambient light increases.
ii. The iris brightens with increasing ambient light, but the pupil does not.
iii. The controlled illumination by LED 108 (and/or LED 110) is reduced by the camera's auto-exposure control algorithm executed by device controller 120, which will reduce pupil and iris brightness in the same proportion. That is, the brightness of the pupil decreases by a greater absolute amount, as it begins at a higher value. This reduces the absolute contrast between the pupil and the iris.

The combination of the above three effects is that under bright-pupil conditions, the pupil size will decrease, which will reduce the bright-pupil effect (however, under very low ambient light conditions, there will be no usable bright The pupillary effect is still present down to small pupil diameters). At the same time, the brightening of the ambient light combined with the adjustment of the LED output control algorithm results in lower pupil brightness and higher iris brightness. All these effects combined act to greatly reduce the bright pupil effect, causing the gray pupil effect to appear at smaller illumination angles.

Thus, the LED output control algorithm should take into account pupil size and iris luminance variations (variation) as well as ambient conditions. Furthermore, there is probably no LED arrangement that can successfully produce a bright pupil over all ambient conditions and resulting pupil sizes and controlled illumination levels.

Referring now to FIG. 14, a graph of detected pupil/iris contrast as a function of the angle between the LED and the camera lens is shown for four different pupil sizes. This graph illustrates the relationship between pupil size, pupil/iris contrast, and LED/camera separation for a given distance. These relationships allow the ambient light level to be estimated in order to achieve the desired iris/pupil contrast, and allow a set of rules to be constructed to control the LED(s). Become.

In some embodiments, camera 106 is configured to capture multiple images per image capture period. In these embodiments, the device controller 120 causes the LEDs 108 to capture at least two images under different lighting and/or image capture conditions within an image capture period, for example by adjusting the output of the LEDs 108 . can be controlled. For example, one image can be captured while LED 108 is driven at a first output level and a second image can be captured while LED 108 is driven at a second output level different from the first output level. captured. This results in two simultaneous or very closely spaced images with different levels of controlled light but a common level of ambient light. In other embodiments, image capture settings such as exposure time or sensor gain may be changed between images.

Vision processor 118 may then perform image subtraction on the two images to produce a resulting image with increased pupillary contrast. In this image subtraction process, the pixel values of corresponding pixels in two images are subtracted to remove the ambient light component and enhance the bright pupil effect.

A similar image subtraction process can be performed for the first embodiment with one or both of LEDs 108 and 110 modulated at different output levels.

The invention described above provides an efficient eye tracking system using pupil/iris contrast that has comparable performance to standard eye tracking systems operating in dark pupil mode but with a 50 percent reduction in package size. Eye tracking may be provided (for the first embodiment). This miniaturization is advantageous in modern vehicles where space on the dashboard instrument panel is at a premium. For the second embodiment (single LED), the package size can be further reduced at the cost of lower performance in small pupil size situations.
[interpretation]

The term "infrared" is used throughout this description and specification. In the scope of this specification, infrared refers to the general infrared region of the electromagnetic spectrum, which includes near-infrared, infrared, and far-infrared frequencies or light waves.

Unless specifically stated otherwise, as will be apparent from the discussion below, throughout this specification the terms "processing", "computing", "calculating", "determining", "analyzing" or the like Discussions using such terms include computers or computers that manipulate and/or transform data expressed as physical quantities, such as electronic, into other data that are similarly expressed as physical quantities. It will be understood to represent the operations and/or processing of a computing system or similar electronic computing device.

Similarly, the terms "controller" or "processor" are used to process electronic data, e.g. It may represent any device or part thereof of a converting device. A "computer" or "computing machine" or "computing platform" may include one or more processors.

References to "one embodiment," "some embodiments," or "an embodiment" throughout this specification may be used to indicate that a particular feature, structure, or characteristic described in connection with an embodiment is the present invention. is meant to be included in at least one embodiment of Thus, the appearances of the phrases "one embodiment," "some embodiments," or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment. . Moreover, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments, as will be apparent to those skilled in the art from this disclosure.

As used herein, unless otherwise stated, the order adjectives “first,” “second,” “third,” etc. used to describe common objects are merely analogous. and that the objects so described must be present in the given order in time, space, hierarchy, or in any other respect. It is not intended to imply that

In the claims that follow and in the description herein, any use of the words comprising, comprising, or comprising are open terms and are meant to include at least the following elements/features. , does not mean to exclude others. Thus, the word comprising, when used in the claims, should not be interpreted as being restricted to the means or elements or steps listed thereafter. For example, the scope of the expression device comprising A and B should not be limited to devices consisting of elements A and B only. Any term including as used herein is still an open term meaning including at least the elements/characteristics following the term, but not meant to exclude others. Thus, "to include" is synonymous with "to comprise" and means "to comprise."

In the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes referred to as a single terminology in order to streamline the disclosure and aid in understanding one or more of the various inventive aspects. summarized in an embodiment, a figure, or a description thereof. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claims require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

Moreover, as will be appreciated by those skilled in the art, some embodiments described herein may include some features, but not other features included in other embodiments, while different embodiments Combinations of the features of are also intended to be within the scope of this disclosure and are intended to form different embodiments. For example, in the following claims, any of the claimed embodiments can be used in any combination.

Many specific details are set forth in the description provided herein. However, it is understood that embodiments of the disclosure may be practiced without these specific details. In other words, well-known methods, structures and techniques have not been shown in detail so as not to obscure the understanding of this description.

Also, it should be noted that the word coupled, when used in the claims, should not be construed as being limited to direct connections only. The terms "coupled" and "connected", as well as their derivatives, may be used. These terms are not intended as synonyms for each other. Thus, the scope of the expression device A coupled to device B should not be limited to devices or systems in which the output of device A is directly connected to the input of device B. That means that there is a path between the output of A and the input of B, which may be a path involving other devices or means. "Coupled" means that two or more elements are in either direct physical, electrical, or optical contact, or that two or more elements are not in direct contact but still It can mean cooperating or interacting with each other.

The embodiments described herein are intended to cover any adaptations or variations of the invention. Although the invention has been described and illustrated in terms of certain exemplary embodiments, it will be appreciated by those skilled in the art that additional embodiments within the scope of the invention can be readily envisioned.

Claims (22)

A method of controlling one or more lighting devices in an eye tracker such that a measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast, the method comprising:
capturing an image of the subject, including one or both of the subject's eyes, for a predetermined image capture period;
illuminating one or both of the subject's eyes from one or more illumination devices during the predetermined image capture period,
illuminating, wherein the at least one lighting device is positioned close enough to the lens of the camera to produce a bright pupil effect;
selectively outputting the output of at least one of said illuminators to produce a bright pupil reflection intensity such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast; and changing to. wherein the output of at least one of the illuminators is selectively based on a direct measure of pupil/iris contrast determined by the intensity of pixels in the pupil region relative to the iris region of one or both eyes of the subject; 2. The method of claim 1, wherein is changed to . wherein the output of at least one of the lighting devices is
i. ambient light measurements,
ii. a measurement of the subject's pupil diameter, and/or iii. 2. The method of claim 1, selectively varied based on one or more of the subject's current or recent gaze direction. 4. The method of claim 3, wherein the ambient light measurements are derived from exposure settings of the camera and/or lighting settings of the one or more lighting devices. 5. The method of any one of claims 1-4, wherein the output of at least one of the lighting devices is selectively varied based on a physiological parameter of the subject. 6. The method of any one of claims 1-5, wherein the output of at least one of the illumination devices is selectively varied at at least two different power levels during an image capture period. 7. The method of claim 6, wherein the camera captures at least two images within an image capture period, the two images captured using different lighting or image capture settings. 8. The method of claim 7, comprising performing image subtraction on the two images to produce a resulting image with increased pupillary contrast. The method of any one of claims 1-8, wherein the eye tracker comprises a single lighting device. 10. The method of any one of claims 1-9, wherein the controller is arranged to modulate the illumination power of the illumination device during an image capture period. The method of any one of claims 1-8, wherein the eye tracker includes two lighting devices positioned at different distances from the camera. 12. The method of Claim 11, wherein selectively varying the output of at least one of the lighting devices comprises deactivating one of the two lighting devices during an image capture period. Method. 11. Each illuminator is positioned close enough to a lens of the camera to produce a brightpupil effect, but at a different distance from the lens to produce different brightpupil reflection characteristics. Or the method according to 12. A system for controlling one or more lighting devices in an eye tracker such that a measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast, said system comprising:
a camera configured to capture an image of a subject within a predetermined image capture period, the image including one or both of the subject's eyes;
one or more lighting devices configured to selectively illuminate one or both eyes of the subject during the predetermined image capture period, at least one of the lighting devices being a bright pupil a lighting device positioned close enough to the lens of the camera to produce an effect;
and adjusting the output of at least one of the illumination devices such that the measured pupil/iris contrast in the captured image produces an intensity of the bright pupillary reflex such that it exceeds a predetermined minimum value of pupil/iris contrast. a controller configured to selectively vary. 15. The system of claim 14, comprising one lighting device. The system includes two lighting devices,
Each of the illuminators is positioned close enough to a lens of the camera to produce a brightpupil effect, but positioned at a different distance from the lens to produce different brightpupil reflection characteristics. 15. The system of claim 14, wherein: 17. The system of claim 16, wherein a first lighting device is positioned at a distance of 3 mm-15 mm from the camera and a second lighting device is positioned at a distance of 7 mm-50 mm from the camera. 18. The system of Claim 16 or 17, wherein the controller is configured to deactivate one of the lighting devices during an image capture period. 19. Any of claims 14-18, wherein the characteristic of the bright pupillary reflex comprises a direct measure of pupil/iris contrast determined by the intensity of pixels in the pupillary region relative to the iris region of one or both eyes of the subject. 2. The system according to item 1. An eye tracking system,
a camera configured to capture an image of a subject within a predetermined image capture period, the image including one or both of the subject's eyes;
One or more lighting devices configured to illuminate one or both eyes of the subject within the predetermined image capture period, wherein at least one of the lighting devices produces a bright pupil effect. a lighting device, positioned sufficiently close to the lens of the camera so as to
A controller, said controller comprising:
performing an eye tracking routine for tracking the eye of the subject by processing the captured image, the eye tracking routine including determining one or more control parameters; executing a tracking routine;
based on the one or more control parameters to produce an intensity of the bright pupillary reflex such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast; and a controller configured to: control the output of one or more lighting devices. A method of controlling two or more lighting devices in an eye tracker such that a measured pupil/iris contrast exceeds a predetermined minimum pupil/iris contrast, the method comprising:
capturing an image of a subject, said image including one or both of said subject's eyes, within a predetermined image capture period;
illuminating one or both eyes of the subject within the predetermined image capture period from a system of two or more illuminators, each of the illuminators for producing a bright pupil effect; illuminating with an illuminator positioned close enough to the lens of the camera at , but positioned at different distances from said lens to produce different bright pupillary reflex characteristics;
selectively outputting the outputs of the two or more illuminators to produce a characteristic bright pupil reflex such that the measured pupil/iris contrast in the captured image exceeds a predetermined minimum pupil/iris contrast; and changing to. 22. Any one of claims 1-21, wherein the output of at least one of the illumination devices is selectively varied based on a measurement of pupillary contrast of the subject's eye from a previous image capture period. A system or method according to paragraph.

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